This application is based on and incorporates herein by reference Japanese Patent Application No. 2002-32458 filed on Feb. 8, 2002.
1. Field of the Invention
The present invention relates to a motor that includes a rotatable shaft, a worm shaft and a clutch, which is arranged between the rotatable shaft and the worm shaft to transmit rotation of the rotatable shaft to the worm shaft and to restrain transmission of rotation from the worm shaft to the rotatable shaft.
2. Description of Related Art
A motor, which includes a motor main body and a speed reducing unit, is used, for example, as a drive source for driving a vehicle power window system installed in a vehicle door. The speed reducing unit reduces a rotational speed of the motor main body and transmits it to an output shaft of the motor. In the motor of the power window system, the weight of a window glass or vibrations of the running vehicle could cause application of rotational force to the output shaft, so that it is necessary to prevent reverse rotation of the output shaft to prevent downward movement of the window glass. To address this, the motor of the power window system is provided with a clutch, which prevents the reverse rotation of the output shaft (or which locks the output shaft).
For example, one previously proposed clutch includes an outer collar, a driving-side rotator, a driven-side rotator, a plurality of balls or cylindrical rollers. The outer collar is non-rotatably arranged. The driving-side rotator is rotated by the motor main body. The driven-side rotator rotates integrally with the output shaft. The balls or cylindrical rollers are arranged between the driven-side rotator and the outer collar. When rotational force is applied from the load side (e.g., from the window glass) to the output shaft, each ball or roller is placed into a wedge-shaped space defined between the driven-side rotator and the outer collar. Thus, rotation of the driven-side rotator is restrained, and the output shaft is locked.
However, the above clutch includes the outer collar, the driving-side rotator, the driven-side rotator and the balls or rollers, so that the number of the components of the clutch is relatively large. Thus, assembly of the clutch is a time consuming task. Furthermore, since the clutch is constructed to lock the output shaft by placing each ball or roller into the wedge-shaped space, the structure of the clutch is complicated, and relatively high precision is required on each component. As a result, productivity of the clutch is relatively low, and thus the manufacturing cost of the clutch is relatively high. This causes an increase in the manufacturing cost of the motor.
Furthermore, smaller and lighter vehicle motors, such as a smaller and lighter motor of the power window system, have been in great demand. Thus, a smaller and lighter clutch installed in such a motor has been also in great demand.
The present invention addresses the above disadvantages. Thus, it is an objective of the present invention to provide a smaller and lighter motor, which can be produced at a lower manufacturing cost, by reducing the number of components of the motor and simplifying a structure of the motor.
To achieve the objective of the present invention, there is provided a motor that includes a motor main body, a speed reducing unit and a clutch. The motor main body includes a rotatable shaft, which is driven to rotate upon energization of the motor main body. The speed reducing unit is connected to the motor main body and includes a worm shaft and an output shaft. The worm shaft is rotatably supported in coaxial relationship to the rotatable shaft. The speed reducing unit transmits rotation of the worm shaft to the output shaft after reducing a rotational speed of the worm shaft. The clutch is arranged between the rotatable shaft and the worm shaft. The clutch includes a driving-side rotator, a driven-side rotator, a spring support and a coil spring. The driving-side rotator rotates integrally with the rotatable shaft. The driven-side rotator rotates integrally with the worm shaft. The spring support includes an inner peripheral surface and is non-rotatably arranged. The coil spring includes a spring main body, first and second driving-side engaging portions, and first and second driven-side engaging portions. The spring main body is received in the spring support and is helically wound. The spring main body includes first and second ends. The first and second driving-side engaging portions are provided in the first and second ends, respectively, of the spring main body and are engageable with the driving-side rotator in a corresponding rotational direction for winding the spring main body and thus for reducing an outer diameter of the spring main body. The first and second driven-side engaging portions are provided in the first and second ends, respectively, of the spring main body and are engageable with the driven-side rotator in a corresponding rotational direction for unwinding the spring main body and thus for increasing the outer diameter of the spring main body. When the driving-side rotator is rotated by the rotatable shaft upon energization of the motor main body, the spring main body is wound to decrease the outer diameter of the spring main body, so that rotation of the driving-side rotator is transmitted to the driven-side rotator through the coil spring. When the driven-side rotator is rotated by an external mechanical rotational force generated outside the motor, the spring main body is unwound to increase the outer diameter of the spring main body, so that a frictional force between an outer peripheral surface of the spring main body and the inner peripheral surface of the spring support is increased to lock the output shaft.
To achieve the objective of the present invention, there is also provided a motor that includes a first shaft, a second shaft and a clutch. The first shaft is driven to rotate upon energization of the motor. The second shaft is rotatably supported in coaxial relationship to the first shaft. The clutch is arranged between the first shaft and the second shaft such that the clutch transmits rotation from the first shaft to the second shaft and restrains transmission of rotation from the second shaft to the first shaft. The clutch includes a driving-side rotator, a driven-side rotator, a spring support and a coil spring. The driving-side rotator is connected to the first shaft to rotate integrally with the first shaft. The driven-side rotator is connected to the second shaft to rotate integrally with the second shaft. The spring support includes a cylindrical wall, which is arranged radially outward of the driving-side rotator and the driven-side rotator and is stationary. The coil spring is axially placed between the driving-side rotator and the driven-side rotator. The coil spring includes a spring main body, at least one driving-side engaging portion and at least one driven-side engaging portion. The spring main body is helically wound and is received inside the cylindrical wall of the spring support in such a manner that the spring main body is resiliently urged against the cylindrical wall when the first shaft and the second shaft are both stopped. The at least one driving-side engaging portion is connected to the spring main body and projects beyond the spring main body in a first axial direction. The at least one driving-side engaging portion is engageable with the driving-side rotator. The at least one driven-side engaging portion is connected to the spring main body and project beyond the spring main body in a second axial direction opposite to the first axial direction. The at least one driven-side engaging portion is engageable with the driven-side rotator. When the driving-side rotator is rotated through energization of the motor, the driving-side rotator engages and moves one of the at least one driving-side engaging portion of the coil spring to wind the spring main body, so that the spring main body is released from the cylindrical wall to rotate integrally with the driving-side rotator, and thus rotation of the driving-side rotator transmitted to the spring main body is further transmitted to the driven-side rotator through one of the at least one driven-side engaging portion of the coil spring to rotate the driven-side rotator and the second shaft. When the driven-side rotator is rotated by an external mechanical rotational force generated outside the motor, the driven-side rotator engages and moves one of the at least one driven-side engaging portion of the coil spring to unwind the spring main body, so that the spring main body is further urged against the cylindrical wall of the spring support to restrain further rotation of the driven-side rotator.